A variety of controlled fuel delivery means exist for reciprocating piston internal combustion engines. One of the most common involves injecting fuel directly into the combustion chamber, as applied in most diesel and gasoline engines. Injectors connected to external pumps are mechanically complex and require complicated control and timing means. One of the limitations of injectors is in their ability to filly disperse liquid fuel inside of the combustion chamber prior to combustion. Injectors need precise nozzles to improve this situation. In some applications, an air and fuel mixture is injected into the combustion chamber which further improves the fuel dispersion, however, external compressors are typically used for this purpose which become more sophisticated when fuel delivery into higher compression ratio engines is required.
Other known methods of delivering fuel in two-stroke engines involve drawing a fuel and air mixture into an area under the primary reciprocating piston, usually the cylinder and crank case, by the vacuum created by the piston's upstroke. The fuel and air mixture is then pressurized by the subsequent down-stroke. When it reaches the maximum pressure below the piston, the fuel and air mixture is allowed into the combustion chamber, above the piston, using a controlled pathway. At this point, fuel and air is delivered into the combustion chamber prior to the compression stroke, due to the piston being in the down position. Consequently, the fuel and air are compressed together in the combustion chamber by the primary piston, therefore, compression can not exceed the pressure where pre-ignition would occur from the adiabatic heating. Disadvantages which result are: lower potential for efficiency gains that are realized with high compression ratios; the need for an ancillary ignition means to control ignition, plus additives in the fuel such as octane. In addition, the air and fuel mixture is typically used to scavenge the exhaust from the combustion chamber, as in the cross flow configuration which tends to allow fuel to be lost through the exhaust port prior to combustion resulting in further efficiency losses.
In four-stroke engines, when injectors are not involved, the typical fuel delivery occurs during the down stroke of the engine's cycle, when fuel enters the combustion chamber prior to compression which requires limiting the compression ratios.